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<table width="100%" summary="page for Penicillin"><tr><td>Penicillin</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Variation in penicillin testing</h2>

<h3>Description</h3>

<p>Six samples of penicillin were tested using the <em>B.
subtilis</em> plate method on each of 24 plates.  The
response is the diameter (mm) of the zone of inhibition
of growth of the organism.
</p>


<h3>Format</h3>

<p>A data frame with 144 observations on the following 3 variables.
</p>

<dl>
<dt><code>diameter</code></dt><dd><p>diameter (mm) of the zone of inhibition of
the growth of the organism.</p>
</dd>
<dt><code>plate</code></dt><dd><p>assay plate.  A factor with levels &lsquo;a&rsquo; to
&lsquo;x&rsquo;.</p>
</dd>
<dt><code>sample</code></dt><dd><p>penicillin sample.  A factor with levels
&lsquo;A&rsquo; to &lsquo;F&rsquo;.</p>
</dd>
</dl>


<h3>Details</h3>

<p>The data are described in Davies and Goldsmith (1972) as
coming from an investigation to &ldquo;assess the
variability between samples of penicillin by the <em>B.
subtilis</em> method.  In this test method a bulk-inoculated
nutrient agar medium is poured into a Petri dish of
approximately 90 mm. diameter, known as a plate.  When
the medium has set, six small hollow cylinders or pots
(about 4 mm. in diameter) are cemented onto the surface
at equally spaced intervals.  A few drops of the
penicillin solutions to be compared are placed in the
respective cylinders, and the whole plate is placed in an
incubator for a given time.  Penicillin diffuses from the
pots into the agar, and this produces a clear circular
zone of inhibition of growth of the organisms, which can
be readily measured.  The diameter of the zone is related
in a known way to the concentration of penicillin in the
solution.&rdquo;
</p>


<h3>Source</h3>

<p>O.L. Davies and P.L. Goldsmith (eds), <em>Statistical
Methods in Research and Production, 4th ed.</em>, Oliver and
Boyd, (1972), section 6.6
</p>


<h3>Examples</h3>

<pre>
str(Penicillin)
require(lattice)
dotplot(reorder(plate, diameter) ~ diameter, Penicillin, groups = sample,
        ylab = "Plate", xlab = "Diameter of growth inhibition zone (mm)",
        type = c("p", "a"), auto.key = list(columns = 3, lines = TRUE,
        title = "Penicillin sample"))
(fm1 &lt;- lmer(diameter ~ (1|plate) + (1|sample), Penicillin))

L &lt;- getME(fm1, "L")
Matrix::image(L, main = "L",
              sub = "Penicillin: Structure of random effects interaction")
</pre>


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